P.N. Davis, 1983. "Gippsland Basin, Southeastern Australia", Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces, A. W. Bally
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The Gippsland basin is located offshore southeastern Australia. It is a wedge-shaped graben, open to the east and bounded to the north and south by east to west trending fault systems. The eastern margin is arbitrarily defined as the limit of continental crust.
The formation of the Gippsland basin is directly related to the eccentric movement of the Tasmanian continental block relative to the Australian and Antarctic blocks during the breakup of Gondwanaland. Rotation of the Tasmanian block to the southwest created a tensional regime in which the Gippsland basin was formed by crustal thinning. This relative movement began in the mid-Cretaceous and ceased in the Eocene when the Tasmanian subplate became part of the Australian plate (Griffiths, 1971).
Initial sedimentation during the Early Cretaceous in the Gippsland basin consisted of a rift valley sequence of non-marine sandstones, siltstones, and shales. Following tilting and, in places, severe erosion at the end of the Early Cretaceous, continued extension and rotation activated a series of northwesterly trending normal faults in the area of the present day offshore Gippsland basin. During this period, the rapidly subsiding basin was filled with continental and marginal marine sediments of the Upper Cretaceous to late Eocene Latrobe Group. The normal faulting and rotation produced an overall wedge-shaped graben, which widened to the southeast and is bounded to the north and south by stable platform areas. Extension and normal faulting diminished markedly after the early Eocene and few faults continued into the late Eocene. From the early Eocene to the Miocene a series of northeasterly trending anticlines formed. Coincident with this folding was the reversal of movement on previously normal faults.
Several author (Richards and Hopkins, 1969; Threlfall et al, 1976) attributed this compression to right lateral transform movement on the east to west basin-bounding fault system. Rapid burial of the Eocene Gippsland basin sediments was effected by progradation of Oligocene to Recent shelfal carbonates onto a sagging continental margin. Submarine channelling due to eustatic sea level changes is prevalent through all the Upper Tertiary sequence.
Both of the above fault types are shown on Line A. The predominant faulting style is normal and down-to-the-south (type 1 on line A). The faulting intensity diminishes in the younger part of the section. One relatively large fault (at shotpoint 2560) continued through to post-Latrobe Group time. All of the normal faults shown on Line A belong to the northwesterly trending "basin forming" fault system.
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Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces
Until a few decades ago, structural and regional geology were traditionally the preserve of field geologists. They usually mapped areas of outcropping deformed rocks and supplemented their work by laboratory studies of rock deformation and by theoretical work. Structural geology became tied to the geology of uplifts, folded belts, and underground mines, all of which were accessible to direct observation. Since World War II we have witnessed a tremendous development of geophysics in oceanography and in petroleum geology. Academic geophysicists in oceanography led their geological colleagues into modern plate tectonics and industry geophysicists developed reflection seismology into a superb structural mapping tool that penetrated the subsurface.
Today we are facing a situation where instruction and textbooks in structural geology are almost entirely dedicated to rock deformation, analytical techniques in detailed field geology and summaries of plate tectonics. Illustrations based on reflection seismic profiles are virtually absent in textbooks of structural geology. These texts illustrate only the parts of the proverbial elephant, together with some conjecture, but without ever offering a glimpse of the whole elephant.
Some of the reason cited for the relative scarcity of published reflection profiles are: 1) the confidentiality of exploration data; 2) difficulties in the photographic reduction and reproduction of seismic profiles for a book format; 3) the two-dimensional nature of vertical reflection profiles; and 4) the obvious distortions in reflection profiles that are typically recorded in time.
The AAPG leadership felt that it was time to attempt to correct the situation and to produce this picture and work atlas. The first volumes, of what may become a series of volumes, are addressing an audience that includes: petroleum geologists concerned with structural interpretations; exploration companies that provide in-house training; the AAPG continuing education program; and academic colleagues interested in updating their curricula in structural geology by inclusion of reflection profiles from the “real world” in their teaching.
The atlas is not meant to be a textbook in reflection seismology (instead we listed some at the end of this introduction) nor a text in structural and/or regional geology. Our intent is simply to provide a teaching tool.